Study On Corrosion Resistance Of Q235 And Gb3091 Steel In Tianjin Geothermal Water

Ag/AgCl reference electrode prepared by electrolytic preparation has been tested in geothermal water at various temperatures from 25℃to 95℃. The reference electrode shows great electrochemical and temperature stability which makes it excellent choice as reference electrode of electrochemistry measurement in geothermal water.Corrosion performance of Q235 and GB3091 sample at various temperatures in geothermal water is evaluated by electrochemical techniques including corrosion potential, the polarization resistance and the polarization curve test. The results show that corrosion potential and the polarization resistance Rp of steels reduce gradually along with temperature increasing. The slope of polarization curves increases when temperature increases. GB3091 steel has better corrosion property than Q235 sample.But both two steels show decreased corrosion performance with elevalued temperature based on Ecorr and Rp measurement. When temperature reach 85℃,materials demonstrates obvious localized corrosion tendency. A characteric temperature is detected for each steel which marks the changed corrosion performance.The immersion test for the two commonly used pipe materials has been carried at the special temperatures for the evaluation of long term corrosion performance.The results of immersion test show that there is the visible scaling layer on the surface of steels after 40 hours of immersion. The scaling layer has good protective effect on steels at the middle of immersion. In later stage the scaling layer cannot protect materials well as the middle stadge. It is easier to form the scaling layer in higher temperature. Moreover scaler layer is easier to be damaged in higher temperature. In contrast, the scaling layer has good protective effect on steels at 65℃.The scaling layer of GB3091 sample is more uniform and densive than that formed on Q235 based on SEM. The morphology of scaling layer at 65℃might be thought as combination of the morphologies of 55℃and 75℃.